Firebase android pagination

Question

I\'m building an app which will show videos stored on firebase. The list of videos needs to be paginated fetching most recent 20 videos at a time.

Here is

Answer 1

This is how I implemented pagination from firebase database. Consider a case if we have 100 messages. So I first load last 20 messages from firebase i.e. 81 to 100. Then on scroll up I call getMoreMessages() function to load next 20 messages which are 61 to 80 and so on.

public class ChatActivity extends Activity {

        String chat_id = "";
        long mTotalChildren = 0;
        boolean loading = false;
        ChildEventListener childEventListenerMain, childEventListenerPager;
        ChatActivity mContext = ChatActivity.this;
        MessageAdapter messageAdapter;
        @BindView(R.id.pb_messages)
        ProgressBar pb_messages;
        @BindView(R.id.ll_audio)
        LinearLayout llAudio;
        @BindView(R.id.tv_record_time)
        AppCompatTextView tvRecordTime;
        @BindView(R.id.tv_cancel)
        AppCompatTextView tvCancel;
        @BindView(R.id.iv_send)
        AppCompatImageView ivSend;
        @BindView(R.id.iv_record)
        AppCompatImageView ivRecord;
        @BindView(R.id.ab_layout)
        AppBarLayout abLayout;
        @BindView(R.id.messages)
        RecyclerView rvMessages;
        @BindView(R.id.iv_chat_icon)
        SimpleDraweeView ivChatIcon;
        @BindView(R.id.iv_camera)
        AppCompatImageView ivCamera;
        @BindView(R.id.iv_gallery)
        AppCompatImageView ivGallery;
        @BindView(R.id.message_input)
        AppCompatEditText messageInput;
        @BindView(R.id.tv_send)
        AppCompatTextView tvSend;
        @BindView(R.id.toolbar_title)
        AppCompatTextView toolbarTitle;
        @BindView(R.id.toolbar_status)
        AppCompatTextView toolbarStatus;
        @BindView(R.id.ll_send)
        LinearLayout llSend;
        int categoryId, senderId, receiverId, offerId;
        String mLastKey;
        LinearLayoutManager layoutManager;
        private ArrayList messageArrayList = new ArrayList<>();
        private ArrayList tempMessageArrayList = new ArrayList<>();

        @Override
        public int getLayoutId() {
            return R.layout.activity_chat;
        }

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

            messageAdapter = new MessageAdapter(mContext, messageArrayList) {

            };

            layoutManager = new LinearLayoutManager(mContext);

            rvMessages.setLayoutManager(layoutManager);
            rvMessages.setItemAnimator(new DefaultItemAnimator());
            rvMessages.setAdapter(messageAdapter);
            rvMessages.setHasFixedSize(true);

            rvMessages.addOnScrollListener(new RecyclerView.OnScrollListener() {
                @Override
                public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                    super.onScrollStateChanged(recyclerView, newState);
                }

                @Override
                public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                    super.onScrolled(recyclerView, dx, dy);

                    if (messageArrayList.size() >= 20 &&
                            !loading && layoutManager.findFirstVisibleItemPosition() == 0 && messageArrayList.size() < mTotalChildren) {

                        loading = true;
                        getMoreMessages();
                    }
                }
            });

            messageAdapter.notifyDataSetChanged();

            //used to scroll up recyclerview when keyboard pops up
            rvMessages.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
                @Override
                public void onLayoutChange(View view, int left, int top, int right, int bottom,
                                           int oldLeft, int oldTop, int oldRight, int oldBottom) {
                    if (bottom < oldBottom) {
                        rvMessages.postDelayed(new Runnable() {
                            @Override
                            public void run() {
                                rvMessages.scrollToPosition(messageArrayList.size() - 1);
                            }
                        }, 100);
                    }
                }
            });

            loading = true;
            getMessages();
        }

        public void getMessages() {

            FirebaseDatabase.getInstance().getReference().child(pathtomsgs).addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    Log.e("childrenCount", String.valueOf(+dataSnapshot.getChildrenCount()));
                    mTotalChildren = dataSnapshot.getChildrenCount();
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });


            Query messageQuery = FirebaseDatabase.getInstance().getReference().child(pathtomsgs).limitToLast(20);

            childEventListenerMain = new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {

                    loading = true;
                    MessageModel messageModel = dataSnapshot.getValue(MessageModel.class);
                    if (messageModel != null) {
                        messageModel.chat_id = chat_id;
                        messageModel.message_id = dataSnapshot.getKey();
                        messageArrayList.add(messageModel);
                        messageAdapter.notifyDataSetChanged();
                        mLastKey = messageArrayList.get(0).message_id;
                        rvMessages.scrollToPosition(messageArrayList.size() - 1);
                    }
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    Toast.makeText(mContext, "Problem loading more images...", Toast.LENGTH_LONG).show();
                }
            };

            messageQuery.addChildEventListener(childEventListenerMain);

            ValueEventListener messageChildSINGLEValueEventListener = new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    pb_messages.setVisibility(View.GONE);
                    System.out.println("We're done loading messages " + dataSnapshot.getChildrenCount() + " items");
                    loading = false;
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            };

            messageQuery.addListenerForSingleValueEvent(messageChildSINGLEValueEventListener);
        }

        public void getMoreMessages() {
            tempMessageArrayList.clear();

            Query messageQuery = FirebaseDatabase.getInstance().getReference().child(pathtomsgs).orderByKey().endAt(mLastKey).limitToLast(20);

            childEventListenerPager = new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    loading = true;
                    MessageModel messageModel = dataSnapshot.getValue(MessageModel.class);
                    if (messageModel != null) {

                        messageModel.chat_id = chat_id;
                        messageModel.message_id = dataSnapshot.getKey();
                        tempMessageArrayList.add(messageModel);
                    }
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    Toast.makeText(mContext, "Problem loading more images...", Toast.LENGTH_LONG).show();
                }
            };

            messageQuery.addChildEventListener(childEventListenerPager);

            ValueEventListener messageChildSINGLEValueEventListener = new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    System.out.println("We're done loading messages " + dataSnapshot.getChildrenCount() + " items");

                    tempMessageArrayList.remove(tempMessageArrayList.size() - 1);

                    messageArrayList.addAll(0, tempMessageArrayList);
                    mLastKey = messageArrayList.get(0).message_id;
                    messageAdapter.notifyDataSetChanged();
                    //rvMessages.scrollToPosition(20);
                    layoutManager.scrollToPositionWithOffset(19, 0);
                    loading = false;
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            };

            messageQuery.addListenerForSingleValueEvent(messageChildSINGLEValueEventListener);
        }


        @Override
        protected void onDestroy() {

            FirebaseDatabase.getInstance().getReference().child(pathtomsgs).removeEventListener(childEventListenerPager);
            FirebaseDatabase.getInstance().getReference().child(pathtomsgs).removeEventListener(childEventListenerMain);

            super.onDestroy();
        }
    }